What Ohio Horse Owners Should Be Aware Of
The United States Department of Agriculture (USDA) and other North, Central and South American officials are closely monitoring cases of the New World Screwworm (NWS). Although NWS has received significant recent attention, it is not a new parasite; it remains endemic in multiple Central American and Caribbean countries. It was previously found in the southern portion of the United States, but was successfully eradicated in the late fifties and early sixties by releasing sterile male flies. The NWS females only mate one time in their entire lifecycle, so if their eggs were fertilized by a sterile (or non-fertile) male, then they would not hatch and the female would die without producing offspring. This sterile insect release technique has successfully eliminated NWS from the United States on multiple occasions following isolated reintroductions.
The New World Screwworm has recently become a hot topic in the press since cases have worked their way north, and have officially been diagnosed in the United States for the first time in over 5 decades. Infestations of NWS larvae, or maggots, can be fatal to animals and, in rare cases, humans. This poses significant animal health concerns as well as economic concerns when food animals such as cattle or swine are affected.
There are several important facts horse owners should know about NWS and how to protect their animals from exposure.
NWS follows a similar life cycle to most other flies. The adult females lay their fertilized eggs near food sources (in this case, flesh). The eggs hatch and larvae feed on the surrounding tissue. NWS larvae prefer the living tissue surrounding wounds, which is a key difference between NWS larvae and other opportunistic fly larvae that feed primarily on dead tissue. They continue to feed until they are mature enough to form small pupae, or pods, where they continue to develop in the environment. Eventually these hatch into adult flies and the lifecycle starts over.
NWS is particularly concerning to our animals because infestations can cause far more significant damage than other species of maggots/flies. Since they prefer living tissue, NWS maggots are particularly destructive, and if large amounts of larvae are present in a wound, they can cause extensive tissue destruction and may lead to serious secondary bacterial infections.
It is important to note that not all maggot infestations are NWS. Multiple fly species will lay eggs in wounds which will cause maggots to be present. A veterinarian should inspect all wounds with maggots present, both for identification purposes and for wound management. There are a few key distinguishing features of NWS flies and larvae that can aid identification, but suspect specimens can also be submitted to diagnostic laboratories for confirmation.
Preventing NWS requires both large-scale and small-scale efforts. On the large-scale front, the USDA has already started releasing sterile (or non-fertile) flies in the areas of known cases to help reduce populations. On small-scale efforts, livestock and pet owners should be diligent about good wound care, fly control, and monitoring.
First, all wounds on animals should be noted as early on as possible so that they can either be primarily closed with stitches, or good management practices can be implemented early to prevent complications such as fly infestation. This may include cleaning, bandaging, or the use of topical products. Owners should be frequently inspecting their animals (this can be done at a time as simple as grooming) and noting wounds early. Once a wound has been identified, caring for it appropriately and monitoring it for signs of infestation are crucial steps. Owners should take care to follow cleaning and bandaging instructions to help prevent contact with flies.
Aerosol Bandage Products
General Wound Care Products
If maggots are noted in or around a wound, a veterinarian should be contacted to help with identification and wound management. There are multiple products that have either been recently approved for emergency use or have been on the market for longer periods of time that are safe for wound treatment. It is important to be aware that not all fly control products are safe to apply directly into wounds. Good fly control can be helpful to limit exposure or accumulation of flies around a property, but it should not be relied upon as the sole means of preventing wound infestations.
What's in Store for Ohio? Understanding the New World Screwworm Threat.
NWS in Ohio?
Luckily for us in Ohio, the NWS is not a fan of our weather! They typically thrive in tropical and subtropical environments, making establishment in Ohio less likely, though not impossible. Travel of horses, pets and people to areas where the NWS is present could be enough to increase risk of exposure. Horses that travel to southern portions of the country should be especially diligent in monitoring their animals before, during and after their travels. Many interstate movements require a Certificate of Veterinary Inspection (‘health certificate’), and veterinarians issuing these certificates must be USDA-accredited. Part of our job is to examine animals for signs of diseases such as NWS and help prevent their spread by restricting the movement of affected animals.
In summary
All in all, we as horse owners should do our part by closely monitoring our animals, being diligent about reporting the presence of maggots within wounds, and caring for them to the best of our ability when they are injured. With good management strategies that prevent the spread of parasites, the large-scale effort to eradicate these flies once again should be successful. If you are concerned about a wound on your animal or need guidance on how to care for a wound, I would strongly recommend you contact your veterinarian for advice and follow-up so we can all do our part in protecting our animals. At the time of writing, no cases of New World Screwworm have been reported in Ohio.
Dr. Vicky Johnson (USDA-accredited veterinarian) from Cleveland Equine Clinic
